Since it’s the spoooookiest time of year, let’s talk about spiders and snakes—two wriggly critters that have long been giving humans the creeps. Most people living in western societies do not live in proximity to dangerous species and have no reason to fear them—yet fear them we do. Just ask Ron Weasley. Or Samuel L. Jackson. As Sarah Gibbens reports for National Geographic, a new study shows that even babies get stressed at the sight of spiders and snakes, suggesting that our aversion to these creepy crawlies could be innate.
Building on previous research showing that both children and adults report a strong dislike for spiders and snakes, researchers at the Max Planck Institute in Germany and Uppsala University in Sweden sought to find out if this fear is a learned or instinctive reaction. So they turned a group of six-month-old babies, who are thought to be too young to have absorbed cultural lessons about these animals.
While sitting on their parents’ lap, 48 little ones were shown two sets of images: spiders and flowers, and snakes and fish. The babies’ parents wore opaque sunglasses that prevented them from seeing the pictures and influencing the adorable test subjects. As the images flashed across a white background, researchers used an infrared eye tracker to measure the dilation of the babies’ pupils. As Stefanie Hoehl, lead researcher of the study, explains during an interview with the CBC, pupillary dilation is associated with the activation of the noradrenergic system in the brain, which is part of our “fight or flight” response.
The results of the study, published in Frontiers in Psychology, showed that the babies reacted with significantly bigger pupils when they were shown images of spiders and snakes, as compared to pictures of flowers and fish. It is difficult to characterize the type of stress the infants were experiencing. But, as the authors of the study write, their dilated pupils indicate “arousal and increased focused attention.”
“[M]echanisms in our brains enable us to identify objects as 'spider’ or 'snake’ and to react to them very fast,” Hoehl says in a Max Planck Institute statement. “This obviously inherited stress reaction in turn predisposes us to learn these animals as dangerous or disgusting.” When the stress reaction is compounded by other factors—a parent losing his or her cool at the sight of a spider, for instance—it “can develop into a real fear or even phobia,” Hoehl says.
Intriguingly, as the statement points out, previous studies have shown that infants do not associate pictures of other potentially dangerous animals, like rhinos and bears, with fear. So why might we be hardwired to freak out over spiders and snakes? Researchers suggest that this reaction has evolved over the many years that humans have co-existed with venomous spiders and snakes—a period of “40 to 60 million years,” Hoehl says, according to the statement, “and therefore much longer than [humans have co-existed] with today’s dangerous mammals.”
Our ancient ancestors had more reason to fear snakes and spiders than we do. But a lingering instinct could explain why harmless house spiders continue to give us the heebie jeebies.